Wind Power

The wind is a by-product of uneven heating of the Earth's atmosphere by the sun, and has a very complex distribution pattern. Though widely spread, winds are most prevalent along coasts, at higher elevations and at higher latitudes.

Siting of a Wind Turbine

The power in the wind is proportional to the cube of its speed; twice the wind speed gives eight times the power. Small differences in average windspeed cause large differences in available wind energy. So, for optimum performance, it is important to find a site which offers the highest overall windspeeds.

Avoid locations with excessive gustiness or turbulence, since they will reduce the output from a wind turbine and lead to undue wear and strain on component parts.

Siting of a wind turbine should take account of exposure to the prevailing winds. Factors such as surface roughness and obstructions are important, e.g. woodland or built up areas will create higher turbulence than open grassland. Cliff tops are to be avoided and wind generators must be sited clear of obstructions to the wind.

A useful rule is to place the wind turbine at a distance from any obstacle (building etc.) of at least ten times the height of the obstacle; or on a tower that is at least twice that height.

Wind speed can increase dramatically with height, especially over rough surfaces, such as in wooded or hilly areas. This means a significant increase in power production can often be obtained for a given cost by using a smaller wind.

The ideal site for a wind turbine is a smooth hill top, with a flat, clear fetch at least in the prevailing wind direction.

Near the top of the hill the wind speeds up significantly and the flow should be reasonably smooth.

In practice, especially for small machines, there is a compromise between choosing the best wind site and other considerations.

Cabling

A voltage drop occurs along wires - in low voltage battery based systems this can be significant, so output cables must be sized appropriately to avoid undue power losses.

Normally underground armoured cable is used and since heavy cable can be expensive this can be a factor in the siting of a wind turbine. However, if higher windspeeds are obtained by siting further away, the resultant increase in power production can compensate for these power losses.

For grid connection of a larger machine, proximity to 11kV power lines is normally required. Conversely this means that good wind sites with existing high voltage supplies can have the potential for the commercial exploitation of wind power.